diff options
Diffstat (limited to 'lib/checksum.c')
| -rw-r--r-- | lib/checksum.c | 52 |
1 files changed, 20 insertions, 32 deletions
diff --git a/lib/checksum.c b/lib/checksum.c index 88ec72a8..f6d74d31 100644 --- a/lib/checksum.c +++ b/lib/checksum.c @@ -52,34 +52,31 @@ in_cksum(void *parg, int nbytes) /* To be consistent, offset is 0-based index, rather than the 1-based index required in the specification ISO 8473, Annex C.1 */ u_int16_t -fletcher_checksum(u_char * buffer, int len, u_int16_t offset) +fletcher_checksum(u_char * buffer, const size_t len, const uint16_t offset) { u_int8_t *p; - int x; - int y; - u_int32_t mul; - u_int32_t c0; - u_int32_t c1; + int x, y, c0, c1; u_int16_t checksum; u_int16_t *csum; - int i, init_len, partial_len; - + size_t partial_len, i, left = len; + checksum = 0; + assert (offset < len); + /* * Zero the csum in the packet. */ csum = (u_int16_t *) (buffer + offset); - *(csum) = checksum; + *(csum) = 0; p = buffer; c0 = 0; c1 = 0; - init_len = len; - while (len != 0) + while (left != 0) { - partial_len = MIN(len, MODX); + partial_len = MIN(left, MODX); for (i = 0; i < partial_len; i++) { @@ -90,27 +87,18 @@ fletcher_checksum(u_char * buffer, int len, u_int16_t offset) c0 = c0 % 255; c1 = c1 % 255; - len -= partial_len; + left -= partial_len; } - - mul = (init_len - offset)*(c0); - - x = mul - c0 - c1; - y = c1 - mul - 1; - - if (y > 0) - y++; - if (x < 0) - x--; - - x %= 255; - y %= 255; - - if (x == 0) - x = 255; - if (y == 0) - y = 1; - + + /* The cast is important, to ensure the mod is taken as a signed value. */ + x = ((int)(len - offset - 1) * c0 - c1) % 255; + + if (x <= 0) + x += 255; + y = 510 - c0 - x; + if (y > 255) + y -= 255; + /* * Now we write this to the packet. * We could skip this step too, since the checksum returned would |